Iodide recovery and boron removal from thin-film transistor liquid crystal display wastewater through forward osmosis

Journal Pre-proof Iodide recovery and boron removal from thin-film transistor liquid crystal display wastewater through forward osmosis Hau-Ming Chang, Shiao-Shing Chen, Zhi-Sheng Cai, Wen-Shing Chang, Saikat Sinha Ray, Nguyen Cong Nguyen, Chi-Wang Li, Mithilesh Paswan PII:

S0959-6526(20)30634-X

DOI:

https://doi.org/10.1016/j.jclepro.2020.120587

Reference:

JCLP 120587

To appear in:

Journal of Cleaner Production

Received Date: 19 June 2019 Revised Date:

7 February 2020

Accepted Date: 13 February 2020

Please cite this article as: Chang H-M, Chen S-S, Cai Z-S, Chang W-S, Ray SS, Nguyen NC, Li C-W, Paswan M, Iodide recovery and boron removal from thin-film transistor liquid crystal display wastewater through forward osmosis, Journal of Cleaner Production (2020), doi: https://doi.org/10.1016/ j.jclepro.2020.120587. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier Ltd.

Author contributions Hau-Ming Chang: Formal analysis, Investigation, Data Curation, Writing - Original Draft, Visualization. Shiao-Shing Chen: Conceptualization, Methodology, Resources, Writing - Review & Editing, Project administration, Visualization, Supervision, Funding acquisition. Zhi-Sheng Cai: Validation, Formal analysis. Wen-Shing Chang: Resources, Supervision. Saikat Sinha Ray: Supervision. Nguyen Cong Nguyen: Supervision, Writing - Review & Editing Chi-Wang Li: Supervision. Mithilesh Paswan: Project administration.

Iodide recovery and boron removal from thin-film transistor liquid crystal

1

display wastewater through forward osmosis

2 3

Hau-Ming Chang a, Shiao-Shing Chen a*, Zhi-Sheng Cai a, Wen-Shing Chang b, Saikat Sinha

4

Ray a, Nguyen Cong Nguyen c, Chi-Wang Li d, Mithilesh Paswan a

5

a

Institute of Environmental Engineering and Management, National Taipei University of Technology, No.1, Sec. 3, Chung –Hsiao E. Rd, Taipei 106, Taiwan, ROC

6 7

b

Environmental Protection Administration, Taiwan, ROC

8

c

Faculty of Environment and Natural Resources, Dalat University, Vietnam

9

d

Department of Water Resources and Environmental Engineering, Tamkang University, New

10

Taipei City, Taiwan

11

*Corresponding author: Shiao-Shing Chen

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(E-mail: [email protected])

13 14 15 16 17 18 19 20

Submitted to

21

Journal of Cleaner Production

22

June, 2019

23 24 25 26

1

1

Wordcount: 6497

2

Abstract

3

For the first time, simultaneous iodide recovery and boron removal from thin-film transistor

4

liquid crystal display wastewater were achieved using forward osmosis because iodide is a

5

precious material and boron is toxic with 1 mg/L discharge standard in Taiwan. Cellulose

6

triacetate and thin-film composite with aquaporin flat sheet membranes were tested for different

7

feed solution, pH levels, and draw solution concentrations. The results indicated that the thin-

8

film composite membrane had high boron and iodide rejections (98.4 % and 98.3 %, respectively)

9

at a pH of 11; however, with a feed boron concentration of 600 mg/L, 9.8 mg/L boron was still

10

present in the draw solution. Cationic surfactant cetyltrimethylammonium bromide was used to

11

enhance the iodide recovery and boron removal efficiencies. Both efficiencies increased to 99.9

12

% with 0.5 mM cetyltrimethylammonium bromide, and only 0.64 mg/L boron was present in the

13

draw solution. In addition, negligible flux reduction was observed for forward osmosis process in

14

the presence of cetyltrimethylammonium bromide. A membrane distillation system was used to

15

concentrate and purify the MgCl2 draw solution. Thus, the hybrid forward osmosis-membrane

16

distillation process can be applied for iodide recovery and boron removal in the thin-film

17

transistor liquid crystal display industry.

18

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Keywords: Forward osmosis; Iodide; Boron; cetyltrimethylammonium bromide; Membrane

20

distillation

21 22 23 2

1

1. Introduction

2

Taiwan is one of the world’s largest providers of thin-film transistor liquid crystal display

3

(TFT-LCD) panels, and the gross production value of Taiwanese TFT-LCD panels reached

4

approximately 264 billion US dollars in 2017 (ITRI, 2018). In the TFT-LCD production process,

5

a key component is the polarizer used for converting an undefined light or mixed polarization

6

beam into a well-defined polarization beam. Iodide and boric acid are essential ingredients for

7

producing polarizers. In the production process, potassium iodide is used to dye and boric acid is

8

used to strengthen the polyvinyl alcohol film of the polarizers (Miyazaki et al., 2010; Nguyen et

9

al., 2016). Thus, this optoelectronic wastewater contains high iodide and boron concentrations.

10

Because raw iodide is limited in nature, expensive, and can only be obtained from natural brine,

11

soda niter, and seaweed, efficient recovery of iodide is important for sustainability. Typically, in

12

the market, products with iodide concentration higher than 6 % are recycled. Boron is a toxic

13

substance, and the Environmental Protection Administration of Taiwan has set the industrial

14

effluent standard for boron as 1 mg/L. Therefore, exploring an efficient and cost-effective

15

method to recover iodide and reduce boron discharge in TFT-LCD wastewater is essential.

16

Various methods have been proposed in the literature for iodide/iodine recovery and boron

17

removal from TFT-LCD wastewater. Currently, thermal distillation and reverse osmosis (RO)

18

are commonly used for iodide recovery in TFT-LCD plants in Taiwan. However, these

19

techniques pose environmental and health risks because of the high energy consumption and

20

possible production of blue iodine gas. Wenten et al.(2012) used iodide ozonation followed by a

21

ceramic membrane to recover iodine by converting iodide to iodine under different pH values.

22

Sánchez-Polo et al.(2006) studied iodide adsorption by using porous silver-activated carbon

23

aerogels according to the electrostatic attraction between silver ions and iodide. Madrakian et 3

1

al.(2012) used modified silica-coated magnetite nanoparticles for iodine removal, and the

2

optimum pH for iodine removal was 7.0–8.0 with 90 % iodine recovery. Gryta (2013) used

3

membrane distillation (MD) to recover iodine from brine with an iodide concentration of 1 g/L,

4

however, the energy consumption and membrane scaling hindered the process. Moreover, Sawai

5

et al.(2012) used permeation and chemical desorption (PCD)/silicone rubber membrane to detach

6

and recover iodine. The PCD method simplified iodine recovery, and the space requirements for

7

this method were low. The aforementioned methods require either intensive energy or chemicals.

8

Therefore, these approaches are unsustainable for iodide recycling in industries. However, these

9

methods require either intensive energies or chemicals, so these approaches are not sustainable

10

for iodide recycle in the industries.

11

Boron is present in natural water in several forms. Boric acid, H3BO3 or B(OH)3, is in

12

equilibrium with borate, and the predominant species is dependent on pH, as shown in Eq. (1)

13

(Xu and Jiang, 2008). The major specie is the uncharged B(OH)3 molecule for pH lower than 9.2,

14

whereas for pH values higher than 9.2, the fully hydrated B(OH)4− anion is the major species.

15

Boric acid and borate undergo condensation reactions to form polymeric oxyanions, as shown in

16

Eq. (2) (Schubert, 2015). Therefore, charge species are formed for pH higher than the pKa.

17

B(OH)3 + H2O ⇌ B(OH)4- + H+

18

2 B(OH)3 + 2 B(OH)4- ⇌ B4O5(OH)42- + 5 H2O

Ka = 10-9.2 M

(1) (2)

19

Boron removal technologies include RO, precipitation, ion exchange, and adsorption (Wang

20

et al., 2014). Typically, for RO, the removal of borate is considerably higher than that of boric

21

acid because of charge repulsion between RO and borate (Öztürk et al., 2008). The general

22

precipitation methods using metal salts must be used at pH levels higher than 9.2 to achieve a

4

1

high boron removal efficiency (Oo and Song, 2009). Typically, precipitation and crystallization

2

are more suitable for water a high concentration of boron than other procedures normally used to

3

manage trace amounts of boron (Yoshikawa et al., 2012). A modified electrocoagulation method

4

was developed for treating 500–1,000 mg/L of boron, and 94 % boron removal was achieved

5

through aluminum precipitation at pH 8.0 (Yilmaz et al., 2007). A method using slaked lime

6

(Ca(OH)2) can achieve a boron removal of 87 % from 750 mg/L boric acid by heating at 45–80

7

°C to form a recyclable precipitate of calcium borate (Irawan et al., 2011b, 2011a). However, the

8

generation of considerable sludge hinders coprecipitation methods that use a high concentration

9

of metal ions.

10

Forward osmosis (FO) is the latest innovation in the field of membrane separation with

11

lesser energy requirement than RO (Cath et al., 2006; Shaffer et al., 2015; Shon et al., 2015).

12

Moreover, FO also offers higher water recovery (Nguyen et al., 2017; Ray et al., 2018). In FO,

13

natural osmosis pressure is the driving force for separation mechanism, and the water flux occurs

14

from a region of low osmotic pressure to high osmotic pressure. Subsequently, the feed solution

15

(FS) is concentrated and the draw solution (DS) is diluted. Therefore, FO can potentially enable

16

(i) low energy consumption, (ii) less fouling than in pressure-driven membrane procedures, and

17

(iii) a high rejection of many contaminants. These notable advantages have encouraged scientists

18

to focus on FO’s research and development, and promising results have been reported in a

19

variety of fields, such as desalination, sludge dewatering wastewater treatment, and power

20

generation (Chung et al., 2012; Lutchmiah et al., 2014). In our previous study (Nguyen et al.,

21

2016), a waste iodide stream was efficiently concentrated using a thin film composite (TFC) FO

22

membrane from 0.6 % to 6 % , which is a valuable product for a TFT-LCD plant that uses

23

another waste stream comprising a high potassium hydroxide concentration similar to the DS

5

1

(pH = 11.5 and total dissolved solids (TDS) = 125.5 g/L). Therefore, a full-scale plant was

2

constructed according to this research result. Although FO was cost-effective compared with

3

traditional techniques such as MD and RO in the full-scale plant, only 90 % of the iodide was

4

recovered and 10 % or approximately 600 mg/L of iodide was passed through the membrane and

5

wasted in the DS. In summary, the energy consumption and chemicals utilization of the forward

6

osmosis-membrane distillation (FO-MD) process was relatively and feasible (Wang et al., 2015;

7

Zhao et al., 2014). Besides, the heat of MD can be obtained from the waste heat, which is readily

8

available in the plant, which not only can decrease the cost for FO-MD system but also meet the

9

concept of the sustainable application (Dow et al., 2017; Ge et al., 2012).

10

Since iodide is a small-size monovalent ion with a radius of 0.21 nm, some iodide can pass

11

through the membrane. Therefore, cationic surfactant cetyltrimethylammonium bromide (CTAB)

12

was utilized in the FS to increase the molecular size by coupling either CTA+ and I-, or CTA+

13

and negatively charged boron species. Surfactant used in FO has never been reported. Surfactant

14

monomer separates into hydrophilic head and hydrophobic tail in aqueous solution (Chang et al.,

15

2015; Gezae Daful et al., 2011). Once the critical micelle concentration (CMC) is reached,

16

amphiphilic molecules would self- assemble into microstructures known as micelles (Faozia et

17

al., 2013; Ghoreishi et al., 2007). Two rival forces occur when micelles are produced: the

18

hydrocarbon–water interactions that cause aggregations and the electrostatic repulsions between

19

the head groups of surfactants. In addition, these forces encourage hydrocarbon tails to react with

20

the micelle and reduce the repulsion of the hydrophilic groups. This study attempted to develop

21

techniques of using surfactants to reduce the quantity of objective pollutants (boron and iodide).

22

The possible formation of micelle assists iodide and boron rejections because the CMC for

23

CTAB is only 1.0 mM. Therefore, the purpose of this study was to evaluate FO as a new

6

1

technology for concentrating iodide and removing boron from polarizer manufacturing

2

wastewater with and without addition of CTAB. Divalent magnesium salt was utilized as DS

3

because of its low reverse salt property (Chen et al., 2015; Johnson et al., 2018; Nguyen et al.,

4

2015). Consequently, the following aspects were explored: (1) effect of the pH, membrane, and

5

DS concentration; (2) effect of the CTAB; (3) membrane fouling for long-term FO operation;

6

and (4) efficiency of DS recovery when using MD.

7

8

2.1 Membranes

9

The thin-film composite membrane (TFC-Aquaporin Inside™ or TFC-AIM) used in this study

10

was purchased from Aquaporin A/S company, Denmark. The membrane had a thickness of

11

approximately 110±15 µm, porosity of 50±2 %, and pore size of 0.3 nm. The appropriate pH

12

range was between pH 3 and 11, and the membrane was negatively charged for pH > 3. The

13

cellulose triacetate (CTA) membrane was obtained from Hydration Technology Innovations,

14

USA. This membrane had a thickness of 144 ± 24 mm, pore size of 0.37 nm, and porosity of

15

50±2 %. The pH range of the membrane was 3-8 (Li et al., 2017; Luo et al., 2018; Singh et al.,

16

2019; Xie et al., 2018). The MD membrane used in this study is polytetrafluoroethylene (PTFE)

17

hydrophobic membranes obtained from the Ray-E Creative company, Taiwan with pore size of

18

0.45 µm.

19

20

21 22

2.2 Experimental system Fig. 1 illustrates the schematic diagram of the FO-MD hybrid system, which comprises a 1 L feed tank, 1 L DS tank, FO membrane cell, and DCMD (direct contact membrane distillation) 7

1

membrane cell. The lab-scale flat sheet FO module was fabricated with an effective area of 41.40

2

cm2. The FS and DS were simultaneously operated by peristaltic pumps (DIGITAL

3

PERISTALTIC PUMP, MP-400D, CHEMIST) to recirculate in the FO system at cross flow rate

4

of 400 cm/min at room temperature. The pH and conductivity of both sides were controlled using

5

the pH/conductivity meter. The FO system was operated in FO mode (active layer facing FS).

6

The original wastewater used in this study contained 600 mg/L boron, 6,200 mg/L iodide, 1950

7

mg/L potassium, and 2 mg/L total organic carbon (TOC) with pH 6.3, which was provide from a

8

TFT-LCD factory located in southern Taiwan. The wastewater had a slight TOC content because

9

of the cellulose triacetate film within the polarizer, and the suspended solids (SS) of this TFT-

10

LCD sewage is 10 mg/L. MgCl2 was used as the DS in this FO system since MgCl2 exhibits the

11

characteristic of high osmosis pressure and lower reverse salt flux (Achilli et al., 2010). In

12

addition, the weighing scale (BW12KH, Shimadzu, Japan) was used for determining the weight

13

of FS. Then, the water flux (Jw) and reverse salt flux (Js) were calculated by monitoring changes

14

of the weight and TDS concentration, as shown in Eq. (3) and (4) (Helfer et al., 2014; Nguyen et

15

al., 2013; Xu et al., 2017), where Vpermeate is the volume of permeated water of membrane, Vpump

16

is the water volume of originally cycled in the system by the pump, A means the area of the

17

membrane, t is the time of operation, Ct represents the concentration of salt. Through detected

18

the change of water volume and salt concentration of membrane two sides, the water flux and

19

reverse salt can be calculated.

20

=

21

=

( (

(

) -



( △ )

×

× × ×

)

)



(3)



(4)

8

1

Surfactant CTAB was used in the FO FS to enhance the iodide recovery and boron removal

2

efficiencies by forming either CTA+-iodide/CTA+-boron or iodide-micelle/boron-micelle

3

complexes in the feed because of the aggregates (Huang and Gu, 1987; Juang et al., 2003;

4

Pavithra et al., 2014). A CTAB concentration range of 0.5–30 mM (182–10.92 g/L) was used to

5

evaluate the effects of the CTAB concentration on the CMC. The DS was diluted after long-time

6

operation, and a PTFE hydrophobic MD with an effective area of 100 cm2 was used to

7

concentrate the DS. The diluted DS of the FO system was used as the feed stream of the DCMD.

8

The driving force of the MD depends on the temperature difference of the two sides. The feed

9

side temperature was controlled at 60 °C, and deionized water was used in the draw side at a

10

temperature of 20 °C. The cross flow rate for both sides of the MD was approximately 18.9 cm/s.

11

Effects of DS concentration, pH, and surfactant concentration were all investigated and each

12

batch experiment was at least operated for three hours and repeated three times. Different

13

concentration of CTAB in the FS of FO process at different pH situation was also conducted.

14

Moreover, the diluted DS was reconcentrated by using the MD process, which can reuse in the

15

FO process.

16

17

2.3 Analytical methods

18

Iodide and boron were measured using an inductively coupled plasma optical emission

19

spectrometer (model optima 8000, PerkinElmer, USA). The detection levels of iodine and boron

20

in the method were both 0.1 mg/L. The iodide and boron of all samples were collected from FS

21

and DS as well as detected after 3 hours of FO operation. The conductivity, pH, and oxidation–

22

reduction potential (ORP) of the system were measured using a pH meter (HANNA instrument,

23

model no. HI 9025), a conductivity meter (SensION156, Hach, USA), and an oxidation– 9

1

reduction potential meter (CON 200/500, CLEAN L’EAU instrument, Taiwan), respectively.

2

The TDS content was determined using the conductivity meter, and the viscosity was measured

3

using a viscosity meter (Sine-wave vibro viscometer, A&D, Model SV-10), and the TDS of feed

4

and permeated sides were monitored every hours during the MD process. The osmotic pressure

5

of the DS was determined using an osmometer (Micro-Osmometer, Model 3320). The particle

6

sizes were analyzed using a nanoparticle sizer (Horiba, model SZ-100, Japan) when the

7

surfactants were added. Furthermore, the membrane surface images with and without surfactants

8

were analyzed through scanning electron microscopy (SEM; Philips XL30).

9

10

3. Results and Discussion

11

To explore the optimum conditions of higher boron removal and iodide recovery of this TFT-

12

LCD wastewater, the operational parameters, such as the pH, membranes, DS concentration,

13

surfactant and DS recovery, were investigated in this section.

14

3.1 Effect of pH and membrane selection

15

Three pH values (7, 9, and 11) were selected for the TFC-AIM membrane and one pH value

16

(7) was selected for the CTA membrane using 1 M MgCl2 as the DS, as displayed in fig. 2(a) and

17

(b). These pH values were selected because the suitable pH range was from 3 to 11 for the TFC-

18

AIM membrane and from 3 to 8 for the CTA membrane (Li et al., 2017; Luo et al., 2018; Singh

19

et al., 2019; Xie et al., 2018). As displayed in fig. 2(a), the iodide rejections were 97.1 %, 97.4

20

%, and 98.3 % when the pH levels were 7, 9, and 11 for the TFC-AIM membranes, respectively,

21

which corresponded to 179.8, 161.2, and 105.4 mg/L of DS effluent, respectively. The iodide

22

removal efficiency increased because of the increased negative charge at high pH values. The

10

1

surface charge of the TFC membrane would be more negative under the high pH level and

2

prevent the anions to pass through the membrane (Xie et al., 2018). Fig. 2(b) illustrates the boron

3

removal of the FO system under different pH levels. The DS effluent still contained 22.2, 15.6,

4

and 9.6 mg/L boron at pH levels of 7, 9, and 11, respectively, even when the removal efficiencies

5

were as high as 96.3 %, 97.4 %, and 98.4 %, respectively. As indicted in previous studies, pH

6

was the essential factor that considerably affected boron rejection (Fam et al., 2014a; Kim et al.,

7

2012). The dominant boron species transformed from B(OH)3 to B(OH)4− or H2BO3− with an

8

increase in the hydration radius when the pH was increased. Then, the boron contaminants could

9

not easily pass through the membrane because of the charge repulsion and large hydration radius.

10

As displayed in fig. 2(a) and (b), the CTA membrane only achieved 94 % iodide rejection and 62

11

% boron removal at pH 7. Therefore, the TFC-AIM membrane was selected for simultaneous

12

iodide recovery and boron removal from TFT-LCD wastewater at pH 11. Moreover, because a

13

high iodide and boron concentration still existed in the DS, efficiency improvement was required

14

(reported in the following section).

15 16

3.2 Effect of draw solute (DS) concentration

17

High DS concentrations enable the rapid concentration of iodide in a TFT-LCD plant using

18

FO; however, the iodide and boron concentrations in the DS must be verified. The flux for

19

various DS concentrations is displayed in fig. 3(a). The water flux increased from 5.6 to 8.0

20

LMH and the reverse salt flux increased from 2.2 to 3.2 g/m2h when the DS concentration was

21

adjusted from 0.5 to 2.0 M. The osmotic pressure increased from the 1,415 to 5,560 mOsm/kg

22

H2O when the DS concentration increased. As displayed in fig. 3(b), the removal efficiencies

23

were all higher than 95 % with 0.5–2.0 M MgCl2 DS; however, the permeated iodide and boron

11

1

concentrations in the DS decreased marginally when the DS concentration was increased. The

2

permeated iodide in the DS decreased from 204.6 to 168.8 mg/L and the permeated boron in the

3

DS decreased from 22.8 to 16.2 mg/L when the DS concentration increased from 0.5 to 2 M. The

4

decrease of boron and iodide in the DS can be explained by three possible phenomenon, as

5

graphically demonstrated in fig 3(c). First, solute transport is relatively stable when the amount

6

of permeated water is proportional to the driving force (Oo and Song, 2009). Therefore, the

7

increase in rejection with the DS concentration can be explained by the increased permeated

8

water diluting the solutes. Second, the transfer of boron and iodide from FS to DS can be

9

blocked by the reverse salt (Fam et al., 2014b; Phillip et al., 2010). The relationship between the

10

water flux and reverse salt flux is shown in Eq.(5). In Eq.(5), Jw denotes the water flux, Js

11

indicates the reverse solute flux, A represents the permeability of water, B refers to the

12

permeability of DS, n is the number of dissolved substances produced by the DS, T is the

13

absolute temperature and Rg is the ideal gas constant. As indicated by Eq. (5), the reversal salt

14

flux increased with an increase in the DS concentration and water flux. Hence, the solute

15

transport pathway of boron and iodide from FS to DS was possibly blocked (Cengeloglu et al.,

16

2008; Kim et al., 2012; Xie et al., 2012). The third possible phenomenon could be that the

17

magnesium ions with reverse positive charge on the feed side balanced the negatively charged

18

iodide to reduce the Donnan effect of iodide and the negatively charge membrane (Cui et al.,

19

2014).

20

! "

≈ $ %&' (

(5)

21

The iodide and boron rejection efficiencies for different DS concentrations were modeled to

22

predict future full-scale plant operations. First, the permeated boron and iodide are expressed in

23

Eq.(6) (Mallevialle et al., 1996): 12

1

)

= *+ × (,-. − ,0. )

(6)

2

where Ji is the solute flux of the FO process, Ki is the mass transfer coefficient of the salt

3

(permeability coefficients), and CFS and CDS are the target salt concentrations of FS and DS,

4

respectively. In this study, the permeability coefficients (Ki) of this TFC-AIM membrane

5

obtained from the basic solution diffusion model

6

(Ki,b) and 2.57 × 10−7 m/s for iodide. The permeability coefficients is the essential parameters of

7

membrane performance, and the permeate concentration of target substance can be simply

8

estimated through Ki. In the FO mode (AL-FS), no notable internal concentration polarization

9

was observed in the system. (Jin et al., 2011). So, the CDS could be defined as Ji/Jw, and then

10

11

= *+ × ∆, were 2.55 × 10−7 m/s for boron

substituted into Eq. (6) to obtain the Eq. (7).

)

=

2) 45 6!

3

× ,-.

(7)

12

The rejection equation is defined in Eq. (8), where the DS dilution was ignored because of the

13

low permeated volume in the FO system. Finally, after substituting Eq. (7) into Eq. (8), the FO

14

rejection model for iodide and boron was obtained.

15

R (%) = 1 −

16

R (%) == 1 −

17

The predicted boron and iodide rejections obtained from Eq. (9) are presented as dashed lines in

18

fig. 3(b) The experimental iodide and boron rejections closely followed the predicted lines with

19

correlation coefficients of 0.9977 (iodide) and 0.9995 (boron), which indicated that the boron

20

and iodide concentrations decreased when the DS concentration was increased.

:;" :<"

=1−

25 25 3 !

5 ! ×:<"

× 100 %

(8)

× 100%

(9)

13

1 2

3.3 Effect of surfactant

3

In the previous two sections, the effects of membrane, pH and DS were discussed and the

4

highest rejections for boron and iodide were 98.4 % and 98.3 %, respectively, at pH 11 for the

5

TFC-AIM membrane, which indicated that 9.8 mg/L boron and 108.5 mg/L iodide were still

6

present in the DS. Because boron and iodide are small-sized monovalent ions (iodide has a radius

7

of 0.22 nm and boron has a radius of 0.18 nm), some iodide and boron still passed through the

8

membrane. Consequently, the application of cationic surfactant CTAB in the feed could enhance

9

the iodide recovery as well as reduce the boron discharge by coupling either CTA+ and I- or

10

CTA+ and negatively charged boron. The effects of CTAB concentration and pH on the iodide

11

recovery and boron rejection were evaluated using 1 M MgCl2 as the DS. Fig 4(a)-(c) displays

12

the effect of 0.5–30 mM CTAB to compare the concentration over and lower than the CMC

13

because CTAB has critical micelle concentration (CMC) of 1.0 mM at pH levels of 7, 9, and 11.

14

As displayed in fig. 4(a), for a pH of 7, the initial contaminant rejections were 96.8 % for boron

15

and 97.1 % for iodide. The rejections considerably increased to 98.3 % (boron) and 99.1 %

16

(iodide) when using 0.5 mM CTAB but did not considerably increase for surfactant

17

concentrations up to 30 mM. The pH level was increased to enhance the charge of the species

18

and membrane. For boron, the removal efficiency notably increased to 99.2 % at a pH of 9 and

19

99.9 % at a pH of 11 when using 0.5 mM CTAB, as shown in fig. 4(b) and (c). Similarly, the

20

iodide removal increased to 98.3 % and 99.9 % when adjusting the pH to 9 and 11, respectively.

21

This phenomenon can be illustrated using the results of previous literatures (Luo et al., 2018; Xie

22

et al., 2018). An increased negative surface potential of the TFC-AIM membrane was achieved

23

when the pH was gradually increased. Because iodide and boron are negatively charged species

14

1

in alkaline conditions, the repulsive force between negatively charged contaminants and the

2

membrane can progressively increase when the pH is increased. However, 9.78 mg/L permeated

3

boron still existed in the DS when pH was adjusted to 11, and CTAB considerably increased the

4

FO removal efficiencies.

5

The increased removals through CTAB enhancement can be explained using the particle

6

size listed in Table 1. According to Table 1, the original particle size of CTAB was

7

approximately 188-280 nm, and the particle size increased to 820-1,460 nm after mixing with the

8

target compounds (iodide and boron). With a pore size of 0.37 nm for the FO, the CTA+ catches

9

the target compounds to form the micelle that has difficulties in passing through the membrane

10

because of its larger structure. Thus, the removals of boron and iodide were improved by CTA+;

11

however, they did not considerably increase for CTAB concentrations higher than 0.5 mM at pH

12

values of 9 and 11.

13

The micelle particles did not considerably affect the experimental water flux. Fig. 4(d)

14

depicts the effect of CTAB on the water flux for 24 hrs, and the water flux without CTAB was

15

declined from 5.4 LMH to 1.9 LMH. This decrease can be attributed to the reduction in the

16

osmotic pressure difference between FS and DS after the long-time operation. Although the

17

water flux with 0.5 mM CTAB reduced from 5.5 LMH to 2.0 LMH, the value is similar to the

18

flux without CTAB. SEM was utilized to observe the membrane surface, and the SEM image of

19

the membrane surface after the experiment with 0.5 mM CTAB is presented in fig 4(d). In

20

contrast to a fresh TFC-AIM membrane (image on the left), the white crystal (micelle) was

21

attached on the active layer of the FO membrane after 24 hrs operation (image on the right).

22

Although the initial concentration of CTAB in the feed (0.5 mM) was lower than the CMC of

23

CTA+ (from 0.9 to 1.0 mM), the feed side concentration increased by more than two times after

15

1

24 hrs operation. However, the flux decline was not affected significantly even with the presence

2

of micelle. This occurs probably because compared with pressure-driven RO, osmotic-driven FO

3

is less susceptible to fouling (Lee et al., 2010; She et al., 2016). Therefore, membrane fouling

4

was not observed when using CTAB in the FS, and the CTA+ micelle did not accrete on the

5

membrane surface and generate major membrane fouling accordingly. Moreover, the

6

concentrated efficiency of wastewater was presented in fig. 5, which presented the iodide of feed

7

solute was concentrated from 0.6 % (6,200 mg/L) to 6 % (61,500 mg/L) with 0.5 mM CTAB at

8

pH 11 after 120 hours operation, and the concentration of boron was increased from 600 mg/L to

9

7,100 mg/L after the FO process, and these results indicated the FO membrane can effectively

10

retain and concentrate iodide for the TFT-LCD plant.

11 12

3.4 Draw solution recovery

13

The DS was diluted in the FO process because of long-time operation and was

14

reconcentrated using the MD process for practical recycling. A 1 L quantity of diluted MgCl2 DS

15

from the FO system was controlled at 60 °C (evaporator side), and 1 L deionized water was used

16

as a cooling stream at 20 °C in the permeated side of MD. Fig. 6(a) illustrates the results for the

17

water flux as well as the TDS in the diluted DS and FS during the MD process. As displayed in

18

fig. 6(a), the water flux reduced from 15.7 to 9.6 LMH after MD operation for 6 hrs, which

19

suggested that membrane wetting and vapor pressure reduction occurred. Furthermore, the TDS

20

content of the diluted DS increased from 79.6 to 123.6 g/L as the distillate TDS increased from

21

0.8 to 2.4 mg/L after 6 hrs, which represents 99.9 % salt removal with MD. Therefore, the water

22

from the diluted DS could be effectively separated and reused to operate the FO system

23

sustainably. The iodide and boron concentration of final effluent were all lower the method

16

1

detection limit, which means the iodide and boron were effectively removed by the FO-MD

2

hybrid system. Besides, Comparing the FO water flux of recovered DS to initial DS, as see in Fig.

3

6(b), the water flux of recovered DS only reduced 2 % and is still capable to utilize again as DS

4

in FO. Overall, through FO-MD hybrid, the recovered DS can be reused in the FO process.

5 6

4. Conclusion

7

Simultaneous iodide recovery and boron removal for a TFT-LCD plant was conducted

8

using an FO system. CTA and TFC-AIM membranes were tested for different DS concentrations.

9

The results indicated that the CTA membrane provided 62 % boron rejection and 94 % iodide

10

removal at a pH of 7 with 1 M MgCl2. The TFC-AIM membrane exhibited 98.4% rejection of

11

boron and 98.3 % rejection of iodide at a pH of 11; however, 9.8 mg/L boron was still present in

12

the DS. Thus, the different concentrations (0.5 mM~30 mM) of surfactant CTAB was used to

13

enhance the iodide recovery and boron removal efficiencies. With the optimum concentration of

14

0.5 mM CTAB, 99.9 % removal efficiencies were achieved for both iodide and boron. The boron

15

effluent concentration in the DS was only 0.64 mg/L without considerable fouling in the

16

presence of the surfactant. Furthermore, the MD system could effectively recover the MgCl2 DS

17

for the FO system.

18

19

5. Acknowledgements

20

Authors are thankful for the funding of experiments from the Ministry of Science and

21

Technology (MOST), Taiwan, Republic of China (ROC), the Institute of Environmental

17

1

Engineering and Management, and the National Taipei University of Technology, under grant

2

number 107-2221-E-027-001-MY3.

3 4

6. Reference

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Figure captions Fig.1 The schematic diagram of FO-MD hybrid system Fig. 2(a). The iodide removal efficiency under different pH of feed solute. (FS: 6,200 mg/L iodide; DS: 1 M MgCl2; temperature 25 oC; crossflow rate 400 cm/min) Fig. 2(b). The boron removal efficiency under different pH of feed solute. (FS: 600 mg/L boron; DS: 1 M MgCl2; temperature 25 oC; crossflow rate 400 cm/min) Fig. 3(a) The water flux, reverse salt flux, and osmotic pressure of different draw solute concentration. (FS: 6,200 mg/L iodide and 600 mg/L boron; DS: MgCl2, pH 7; cross flow rate = 400 cm/min). Fig. 3(b) The predicted rejection and real removal of boron and iodide by TFC-AIM membrane. (FS: 600 mg/L boron and 6,200 mg/L iodide, DS: MgCl2; cross flow rate = 400 cm/min; Ki,b = 2.55 10-7 m/s; Ki,i = 2.57 10-7 m/s) Fig. 3(c) The schematic diagram of solute transport when the DS concentration increased. Fig. 4(a). The efficiency of containments removal at different surfactant concentration. (FS: 600 mg/L boron and 6,200 mg/L iodide, pH 7, DS: 1 M MgCl2; cross flow rate = 400 cm/min) Fig. 4(b). The efficiency of containments removal at different surfactant concentration. (FS: 600 mg/L boron and 6,200 mg/L iodide, pH 9, DS: 1 M MgCl2; cross flow rate = 400 cm/min) Fig. 4(c). The efficiency of containments removal at different surfactant concentration. (FS: 600 mg/L boron and 6,200 mg/L iodide, pH 11, DS: 1 M MgCl2; cross flow rate= 400 cm/min) Fig. 4(d) The water flux with and without the presence of CTAB in the wastewater. (FS: 600 mg/L boron and 6,200 mg/L iodide, DS: 1 M MgCl2; cross flow rate = 400 cm/min)

Fig. 5 The concentration of iodide and boron when the long time FO operation. (Initial FS: 600 mg/L boron and 6,200 mg/L iodide with 0.5 mM CTAB at pH 11, DS: 1 M MgCl2; cross flow rate = 400 cm/min) Fig. 6(a) The water flux and TDS of MD process. (FS: diluted draw solute; feed temperature = 60 oC; distillate temperature = 20 oC; crossflow rate 18.9 cm/s; PTFE membrane with pore size 0.45 µm) Fig. 6(b) The water flux of original DS and recovery DS. (FS: 600 mg/L boron and 6,200 mg/L iodide; cross flow rate = 400 cm/min.)

Figures:

Fig.1

Permeated iodide concentration (mg/L) Iodide rejection (%) 100

80 300

60 200 40

100 20

0

0 TFC-AIM (pH 7)

TFC-AIM (pH 9)

TFC-AIM (pH 11)

Fig.2(a).

CTA (pH 7)

Iodide rejection (%)

Permeated iodide concentration (mg/L)

400

Permeated boron concentration (mg/L) 100

200

80

150

60

100

40

50

20

0

0 TFC-AIM (pH 7)

TFC-AIM (pH 9)

TFC-AIM (pH 11)

CTA (pH 7)

Fig. 2(b).

4

8

Water flux (LMH)

Reverse salt flux (g/m2h)

8

6

6000

10 Water flux Reverse salt flux Osmotic pressure

5000

4000 6 3000 4 2000

2

2

0

0

1000

0 0.5

1.0

1.5

Draw solute concentration (M)

Fig. 3(a).

2.0

Osmotic pressure (mOsm/kg H2O)

10

Boron rejection (%)

Permeated boron concentration (mg/L)

Boron rejection (%) 250

70

60

60

500 Permeated iodide concentration Permeated boron concentration Experimental iodide rejection Experimental boron rejection Predicted boron rejection Predicted iodide rejection

400

300

50

40

30 200 20 100

10

0

0 0.5

1.0

1.5

Draw solute concentration (M)

Fig. 3(b).

Fig. 3(c).

2.0

100

90

80

70

60

Boron rejection (%)

80

70

Permeated boron concentration (mg/L)

Iodide rejection (%)

90

600

Permeated iodide concentration (mg/L)

100

85

80

30

250

25 200

Permeated ioidie concentration Permeated boron concentration Iodide rejection Boron rejection

150

20

15 100 10 50

5

0

100

0 0 mM

0.5 mM

1 mM

3 mM

5 mM

10 mM

98

96

94

Boron rejection (%)

90

92

90

30 mM

CTAB concentration

Fig. 4(a).

85

80

30

250

25 200 Permeated iodide concentration Permeated boron concentration Iodide rejection Boron rejection

150

20

15 100 10 50

5

0

0 0 mM

0.5 mM

1 mM

3 mM

5 mM

CTAB concentration

Fig. 4(b).

10 mM

30 mM

100

98

96

94

92

90

Boron rejection (%)

90

35

Permeated boron concentration (mg/L)

95

300

Permeated iodide concentration (mg/L)

100

Iodide rejection (%)

Iodide rejection (%)

95

35

Permeated boron concentration (mg/L)

300

Permeated ioidie concentration (mg/L)

100

94

92

90

30 150

Permeated iodide concentration Permeated boron concentration Iodide rejection Boron rejection

25

20

100 15

10 50 5

0

0 0 mM

0.5 mM

1 mM

3 mM

5 mM

CTAB concentration

Fig. 4(c).

Fig. 4(d).

10 mM

30 mM

99

98

97

96

95

Boron rejection (%)

96

100

35

Permeated boron concentration (mg/L)

Iodide rejection (%)

98

200

Permeated iodide concentration (mg/L)

100

Fig. 5.

Water flux (LMH)

16

120

14

110

12

100

10

90

8

80

6

70 0

1

2

3

4

Time (hrs)

Fig. 6 (a).

5

6

3.0

2.5

2.0

1.5

1.0

0.5

TDS of distillate (mg/L)

130 Water flux TDS of diluted draw solution TDS of distillate

TDS of diluted draw solution (g/L)

18

Fig. 6(b).

Table: Table 1. Particle size of CTAB in the experiment (pH 9，Particle Refractive Index：1.435-0.000i)

CTAB concentration

CTAB average particle size

Average particle size after

(mM)

（nm） ）

CTAB doped with Boron and Iodide（ （nm） ）

0.5

264.7

928.7

1

270.5

829.9

3

257.5

868.0

5

179.5

1,398.9

10

188.0

1,243.6

30

275.5

1,456.3

Highlights Iodide recovery and boron removal were achieved from the TFT-LCD wastewater. Surfactant CTAB was used to enhance the iodide recovery and boron removal. The removals were increased to 99.9% with 0.64 mg/L boron in the DS by 0.5 mM CTAB. FO-MD can be used for iodide recovery and boron removal in the TFT-LCD industry.

Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: